The present invention relates to a press die for piercing operation in a press machine.
In general, a press die for piercing operation comprises an upper die and a lower die, a die bush with a hollow bore imbeddedly fixed to and supported by the lower die, a pad for clamping a workpiece or blank fixedly against the lower die so that a portion of the workpiece to be pierced is positioned directly over the bore of the die bush, and a punch actuated by a portion of the upper die to carry out a piercing action toward and into the die bush through the workpiece. The punch thus operates cooperatively with the die bush to punch out a hole in the workpiece. That is, piercing is accomplished.
As described in detail hereinafter with reference to drawings, certain features of the press die of the prior art have given rise to a number of disadvantages. A feature of the known die is that the punch is held by a punch holder. The punch holder in turn is fixed by bolts and a knock pin to a part of the upper die. Such attachment of the punch holder and the punch to the upper die makes possible adjustment to a limited degree of the position of the piercing portion of the punch relative to the bore of the die bush. That is, the adjustment of the clearance and cutting-edge alignment between the punch and the die bush must be accurate. Otherwise burrs will be formed on the rim of the pierced hole of the workpiece. However, such adjustment is troublesome, requiring much labor and time.
Furthermore, much labor is required for the drilling and tapping of holes for the bolts and knock pin in the fabrication and assembly of the die. Such mode of construction is also undesirable from the view point of maintenance and servicing.